Circuit Device and Head-Up Display Apparatus

ABSTRACT

A circuit device is used for a head-up display apparatus. The circuit device includes a distortion correction circuit and an error detection circuit. The distortion correction circuit performs a distortion correction on input image data as image data of an input image and outputs output image data as image data of an output image after the distortion correction. Respective first divisional areas of a first divisional area group formed by division of the input image correspond to respective second divisional areas of a second divisional area group in the output image in the distortion correction. Here, the error detection circuit performs detection of a distortion correction error of the respective second divisional areas by comparing the input image data of the respective first divisional areas to the output image data of the respective second divisional areas.

The present application is based on, and claims priority from JPApplication Serial Number 2021-176092, filed Oct. 28, 2021, thedisclosure of which is hereby incorporated by reference herein in itsentirety.

BACKGROUND 1. Technical Field

The present disclosure relates to a circuit device, a head-up displayapparatus, etc.

2. Related Art

JP-A-2020-101784 discloses a circuit device used for a head-up display.The circuit device includes an error detection circuit and a processingcircuit. The error detection circuit detects an occurrence of a firstglare error when a glare index value obtained from head-up display imagedata exceeds a first threshold. The processing circuit performsprocessing for the first glare error when the occurrence of the firstglare error is detected.

In a head-up display, a distortion correction to provide reversedistortion to image distortion at projection to an image is performedand an undistorted image is projected. When it is desired to detect aprocessing error of the distortion correction, if common error detectionfor the entire screen of the head-up display is performed, there is aproblem that only the common processing for dealing with an error forthe entire screen can be performed. The above mentioned JP-A-2020-101784is an example of glare detection, and a glare index value is obtainedfrom image data of the entire screen and an occurrence of a first glareerror is detected based on the glare index value. That is, common glaredetection for the entire screen of the head-up display is performed andthere is a problem that only the common processing for dealing with anerror for the entire screen can be performed.

SUMMARY

An aspect of the present disclosure relates to a circuit device used fora head-up display apparatus, including a distortion correction circuitperforming a distortion correction on input image data as image data ofan input image and outputting output image data as image data of anoutput image after the distortion correction, and an error detectioncircuit, when respective first divisional areas of a first divisionalarea group formed by division of the input image correspond torespective second divisional areas of a second divisional area group inthe output image in the distortion correction, performing detection of adistortion correction error of the respective second divisional areas bycomparing the input image data of the respective first divisional areasto the output image data of the respective second divisional areas.

Another aspect of the present disclosure relates to a head-up displayapparatus including the above described circuit device, a processingdevice controlling the circuit device, and a display device projecting adisplay image based on the output image data from the circuit device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a display example of an HUD.

FIG. 2 shows a configuration example of a head-up display apparatus anda circuit device.

FIG. 3 is a diagram for explanation of an operation of an errordetection circuit.

FIG. 4 shows a detailed configuration example of an error determinationunit.

FIG. 5 is a diagram for explanation of an operation of the errordetermination unit.

FIG. 6 shows a first detailed configuration example of the circuitdevice.

FIG. 7 shows a second detailed configuration example of the circuitdevice.

FIG. 8 shows a third detailed configuration example of the circuitdevice.

FIG. 9 shows a fourth detailed configuration example of the circuitdevice and a detailed configuration example of a display device.

FIG. 10 shows a first example of processing of dealing with a distortioncorrection error with respect to each area.

FIG. 11 shows a second example of the processing of dealing with thedistortion correction error with respect to each area.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

As below, preferred embodiments of the present disclosure will beexplained in detail. The following embodiments do not unduly limit thedetails described in the appended claims and not all configurationsdescribed in the embodiments are essential component elements.

1. First Configuration Example of Display System and Circuit Device

FIG. 1 shows a display example of an HUD. HUD is an abbreviation forhead-up display. As below, a head-up display may be appropriatelyabbreviated as an HUD.

The HUD includes a liquid crystal panel, a backlight device, and areflection plate. The backlight device outputs light, the lighttransmitted through the liquid crystal panel is reflected toward ascreen by the reflection plate, and the light reflected by the screenenters eyes of a user. Thereby, virtual display objects 6 correspondingto display objects displayed on the liquid crystal panel are projectedin the field of view of the user. The virtual display objects 6 overlapwith a real space as the background of HUD display. Within a displayarea 5 of the HUD, an area where the virtual display objects 6 are notdisplayed is an area in a transparent color without any display since itis in a non-transmissive state in the liquid crystal panel, and thebackground is seen as it is.

As described above, the distortion correction is performed in imageprocessing of the HUD. When a processing error occurs in the distortioncorrection, a display object having a different shape, size, or colorfrom that of the display object 6 supposed to be displayed may bedisplayed or the display object 6 supposed to be displayed may not bedisplayed. Accordingly, in the embodiment, a circuit device used for theHUD detects an error of the distortion correction. Here, it is desirablethat a portion with an error in the distortion correction processing isdetectable within the display area 5 of the HUD. As an example,processing of dealing with an error of setting the HUD display to betransparent when the error occurs is considered, however, in view ofcontinuation of information presentation to the user, it is desirablethat the HUD display is maintained as much as possible. When the portionwith an error in the distortion correction processing is detectable, theHUD display of the entire screen is not set to be transparent, but theHUD display of only the portion with the error may be set to betransparent and the HUD display of other portions may be maintained.

FIG. 2 shows a configuration example of a head-up display apparatus 50and a circuit device 100 used for the head-up display apparatus 50 inthe embodiment. The head-up display apparatus 50 includes a displaydevice 30, the circuit device 100, and a processing device 200.

The processing device 200 transmits input image data IMA as image dataof an input image to the circuit device 100. The processing device 200is the so-called SoC e.g. a processor such as a CPU or a microcomputer.SoC is an abbreviation for System on Chip. CPU is an abbreviation forCentral Processing Unit.

The circuit device 100 includes an input circuit 105, a distortioncorrection circuit 110, an error detection circuit 320, and an outputcircuit 130. The circuit device 100 is e.g. an integrated circuit devicein which a plurality of circuit elements are integrated on asemiconductor substrate.

The input circuit 105 receives the input image data IMA from theprocessing device 200. The input circuit 105 may be a receiving circuitof various communication interfaces and, as an example, a receivingcircuit of LVDS, DVI, display port, GMSL, or GVIF. LVDS is anabbreviation for Low voltage differential signaling, DVI is anabbreviation for Digital Visual Interface, GMSL is an abbreviation forGigabit Multimedia Serial Link, and GVIF is an abbreviation for GigabitVideo InterFace.

The distortion correction circuit 110 performs a distortion correctionon the input image data IMA using coordinate transformation betweenpixel coordinates in the input image data IMA and pixel coordinates inoutput image data IMB and outputs a result thereof as the output imagedata IMB as image data of an output image. The distortion correction isan image correction to form HUD display with no or reduced distortion byproviding reverse image distortion to image distortion when an imagedisplayed on a display panel is projected on the image. The imagedistortion by projection includes one or both of image distortion due toa curved surface of the screen and image distortion due to an HUDoptical system.

The distortion correction circuit 110 corresponds to a reverse warpengine or a forward warp engine. Reverse warp is warp processing ofcoordinate-transforming the pixel coordinates on the output image dataIMB into reference coordinates corresponding thereto and obtaining pixeldata of the output image data IMB from pixel data of the input imagedata IMA at the reference coordinates. Forward warp is warp processingof coordinate-transforming the pixel coordinates on the input image dataIMA to movement destination coordinates corresponding thereto andobtaining pixel data of the output image data IMB at the movementdestination coordinates from pixel data of the input image data IMA atthe pixel coordinates. The coordinate transformations in the reversewarp and the forward warp are defined by warp parameters. The warpparameters are a table in which coordinates on the input image data IMAare correlated with coordinates on the output image data IMB, a tableshowing amounts of movement between the coordinates on the input imagedata IMA and the coordinates on the output image data IMB, coefficientsof a polynomial correlating the coordinates on the input image data IMAwith the coordinates on the output image data IMB, or the like.

Note that the distortion correction circuit 110 and the error detectioncircuit 320 are logic circuits. The respective distortion correctioncircuit 110 and error detection circuit 320 may be formed as individualcircuits or the distortion correction circuit 110 and the errordetection circuit 320 may be formed as an integrated circuit byautomatic placement and routing or the like. Alternatively, part or allof these logic circuits may be realized by a processor such as a DSP.DSP is an abbreviation for Digital Signal Processor. In this case,programs and command sets in which functions of the respective circuitsare described are stored in a memory, and the programs and command setsare executed by the processor and the functions of the respectivecircuits are realized.

The output circuit 130 transmits the output image data IMB to thedisplay device 30. The output circuit 130 may be a transmitting circuitof various communication interfaces and, as an example, a transmittingcircuit of LVDS, DVI, display port, GMSL, or GVIF.

The display device 30 displays a virtual image in the field of view ofthe user based on the output image data IMB received from the circuitdevice 100. The display device 30 includes a display controller, adisplay driver, an image display device, and an optical system. Notethat the configuration of the display device 30 is not limited to that,but the circuit device 100 may have a function of the displaycontroller, for example.

The display controller performs image data transmission to the displaydriver and display timing control based on the received output imagedata IMB. The display driver drives the image display device based onthe image data from the display controller and the display timingcontrol, and the image display device displays an image corresponding tothe output image data IMB. The optical system includes a reflectionplate etc. and projects the image displayed by the image display deviceon the screen. The screen may be a transparent member on which an imageis projected having a projection surface reflecting the projected light.For example, the screen is a windscreen of a moving body on which theHUD is mounted. The image display device includes e.g. a liquid crystaldisplay panel and a backlight device. Alternatively, the image displaydevice may include a laser source, a mirror reflecting a laser, and anactuator driving the mirror to scan with the laser. Alternatively, theimage display device may be a digital mirror device including a lasersource, an array of micromirrors, and an actuator driving the respectivemicromirrors. Alternatively, the image display device may be aself-emitting display panel such as an OLED display panel. OLED is anabbreviation for Organic Light Emitting Diode.

The error detection circuit 320 of the circuit device 100 performs errordetection of a distortion correction by comparing the input image dataIMA to the output image data IMB. The error detection of the distortioncorrection is to detect whether or not the distortion correction in thedistortion correction circuit 110 is normally performed. Note that“normally” here is not limited to a case where the distortion correctionis performed without an error of only one bit, but includes a case wherethe input image data IMA and the output image data IMB substantiallycoincide with each other to the degree that the input image and thedisplay image of the HUD may be regarded as substantially the sameimages.

FIG. 3 is a diagram for explanation of an operation of the errordetection circuit 320. The error detection circuit 320 includes an areadetermination unit 321 and an error determination unit 322. Note thatdashed lines show divisional areas, but are not actually displayed.

As shown in FIG. 3 , the area determination unit 321 sets a firstdivisional area group formed by division of an input image. Therespective first divisional areas of the first divisional area group areshown by ARA. Specifically, the divisional areas are set by a pluralityof straight lines in horizontal scanning directions and a plurality ofstraight lines in vertical directions. The circuit device 100 includesan area setting register (not shown), the processing device 200 writessetting information of the first divisional area group in the areasetting register, and the area determination unit 321 sets the firstdivisional area group based on the setting information. Note that FIG. 3shows an example of 6×4 divisions of the image, however, the number ofdivisions is not limited to that. Further, FIG. 3 shows an example ofequal division of the image in the horizontal directions and thevertical directions, however, the image may be unequally divided. Forexample, the image may be finely divided in the vertical directions inthe upper part of the screen or finely divided in the center part in thehorizontal directions.

The input image is HUD-projected after the distortion correction in thereverse direction to the distortion by HUD projection, and displaywithout distortion like the input image is obtained. That is, settingthe first divisional area group in the input image is equivalent tosetting a divisional area group in the HUD display. The divisional areagroup in the HUD display is referred to as “third divisional area group”and the respective third divisional areas are shown by ARH. The shape ofthe third divisional area ARH is the same as that of the firstdivisional area ARA corresponding to the third divisional area ARH.Coordinates (u,v) on the input image are correlated with coordinates(x,y) on the output image by coordinate transformation of the distortioncorrection. The output image is divided into a second divisional areagroup corresponding to the first divisional area group by thecorrelation of the coordinates. The respective second divisional areasof the second divisional area group are shown by ARB. The seconddivisional area ARB has a shape distorted by the distortion correction.

As described above, the respective first divisional areas ARA of theinput image, the respective second divisional areas ARB of the outputimage, and the respective third divisional areas ARH of the HUD displayare correlated with one another. Thereby, the error detection circuit320 may detect an error of the distortion correction with respect toeach third divisional area ARH of the HUD display by comparing the inputimage data IMA of the first divisional area ARA to the output image dataIMB of the second divisional area ARB corresponding to the firstdivisional area ARA.

Specifically, the area determination unit 321 determines the firstdivisional area ARA of the first divisional area group to which thecoordinates (u,v) on the input image corresponding to the coordinates(x,y) on the output image belong. When the plurality of coordinates(u,v) corresponding to the plurality of coordinates (x,y) belong to thesame first divisional area ARA, the area determination unit 321 judgesthat the plurality of coordinates (x,y) belong to the same seconddivisional area ARB. In this manner, the second divisional area ARB ofthe output image corresponding to the first divisional area ARA set inthe input image is judged. The pixel data of the input image data IMA atthe coordinates (u,v) is referred to as PA(u,v), and the pixel data ofthe output image data IMB at the coordinates (x,y) is referred to asPB(x,y). The error determination unit 322 determines whether or not adistortion correction error occurs in the second divisional area ARBfrom the pixel data PA(u,v) belonging to the first divisional area ARAand the pixel data PB(x,y) belonging to the second divisional area ARBcorresponding to the first divisional area ARA. The error determinationunit 322 executes the error determination on the respective seconddivisional areas ARB.

In the above described embodiment, the circuit device 100 is used forthe head-up display apparatus 50. The circuit device 100 includes thedistortion correction circuit 110 and the error detection circuit 320.The distortion correction circuit 110 performs the distortion correctionon the input image data IMA as the image data of the input image andoutputs the output image data IMB as the image data of the output imageafter the distortion correction. The respective first divisional areasARA of the first divisional area group formed by division of the inputimage correspond to the respective second divisional areas ARB of thesecond divisional area group in the output image in the distortioncorrection. Here, the error detection circuit 320 may perform detectionof the distortion correction errors of the respective second divisionalareas ARB by comparing the input image data IMA of the respective firstdivisional areas ARA to the output image data IMB of the respectivesecond divisional areas ARB.

According to the embodiment, when a distortion correction error occursin a part of an image, an area where the error occurs may be detected.Specifically, by comparison between the input image data IMA of therespective first divisional areas ARA and the output image data IMB ofthe respective second divisional areas ARB, the first divisional areaARA and the second divisional area ARB at a lower degree of coincidenceis detected as an area where a distortion correction error occurs.Thereby, the processing of dealing with an error can be performed onlyon the area where the distortion correction error is detected. Forexample, as will be described later with reference to FIGS. 9 to 11 ,the processing device 200 transparently displays the area determined ashaving the distortion correction error not to display the image in thearea where the distortion correction error occurs and maintains the HUDdisplay in the other areas, and the information presentation to the usermay be continued.

Further, according to the embodiment, the output image is a distortedimage due to the distortion correction, and the first divisional areagroup is set in the undistorted input image. Here, the respective firstdivisional areas ARA of the first divisional area group formed bydivision of the input image correspond to the respective seconddivisional areas ARB of the second divisional area group in the outputimage in the distortion correction, and the error detection circuit 320may compare the input image data IMA of the respective first divisionalareas ARA to the output image data IMB of the respective seconddivisional areas ARB using the correlations.

Further, in the embodiment, the error detection circuit 320 determinescorrelations between the respective first divisional areas ARA and therespective second divisional areas ARB based on correlation informationbetween coordinates GZA=(u,v) on the input image and coordinatesGZB=(x,y) on the output image correlated by the distortion correction.

According to the embodiment, coordinate transformation between thecoordinates GZA=(u,v) on the input image and the coordinates GZB=(x,y)on the output image is performed in the coordinate transformation of thedistortion correction. The error detection circuit 320 may determine thefirst divisional area ARA to which the coordinates GZA=(u,v) on theinput image corresponding to the coordinates GZB=(x,y) on the outputimage belong using the correlation. Thereby, the first divisional areaARA on the input image is correlated with the second divisional area ARBon the output image.

2. Detailed Configuration Example of Error Determination Unit

FIG. 4 shows a detailed configuration example of the error determinationunit 322. The error determination unit 322 includes a histogramcalculation section HSA, a histogram calculation section HSB, and acomparison section CP.

FIG. 5 is a diagram for explanation of an operation of the errordetermination unit 322. Here, n first divisional areas ARA1 to ARAn areset in the input image. The second divisional area corresponding to thefirst divisional area ARAk is shown by ARBk. n is an integer equal to orlarger than 2 and k is an integer equal to or larger than 1 and equal toor less than n.

The histogram calculation section HSA calculates a histogram from theinput image data IMA of the first divisional area ARAk. The histogramshows a normalized pixel number having respective pixel values. Thenormalized pixel number is obtained by division of a pixel number havingrespective pixel values by a total pixel number of the first divisionalarea ARAk. FIG. 5 shows a single histogram for the first divisional areaARAk, however, the histogram calculation section HSA obtains a histogramof R pixel values, a histogram of G pixel values, and a histogram of Bpixel values.

The histogram calculation section HSB calculates a histogram from theoutput image data IMB of the second divisional area ARBk. The normalizedpixel number is obtained by division of a pixel number having respectivepixel values by a total pixel number of the second divisional area ARBk.FIG. 5 shows a single histogram for the second divisional area ARBk,however, the histogram calculation section HSB obtains a histogram of Rpixel values, a histogram of G pixel values, and a histogram of B pixelvalues.

The comparison section CP compares the histogram of the first divisionalarea ARAk to the histogram of the second divisional area ARBk. Thecomparison section CP judges that an error occurs in the distortioncorrection of the second divisional area ARBk when the histogram of thefirst divisional area ARAk and the histogram of the second divisionalarea ARBk are not the same. Note that the histograms being the sameincludes histograms being substantially the same.

Specifically, the comparison section CP obtains differences between thehistogram of the R pixel values, the histogram of the G pixel values,and the histogram of the B pixel values of the first divisional areaARAk and the histogram of the R pixel values, the histogram of the Gpixel values, and the histogram of the B pixel values of the seconddivisional area ARBk. The following expression (1) shows a mathematicalexpression for obtaining a difference SADk.

$\begin{matrix}{{SADk} = {{\sum\limits_{i = 0}^{15}{❘{{{ARAk\_ rbin}(i)} - {{ARBk\_ rbin}(i)}}❘}} + {\sum\limits_{i = 0}^{15}{❘{{{ARAk\_ gbin}(i)} - {{ARBk\_ gbin}(i)}}❘}} + {\sum\limits_{i = 0}^{15}{❘{{{ARAk\_ bbin}(i)} - {{ARBk\_ bbin}(i)}}❘}}}} & (1)\end{matrix}$

In the above expression (1), ARAk_rbin(i) shows a normalized pixelnumber of a pixel value i in the histogram of the R pixel values of thefirst divisional area ARAk. Here, i is an integer from 0 to 15.ARBk_rbin(i) shows a normalized pixel number of the pixel value i in thehistogram of the R pixel values of the second divisional area ARBk.ARAk_gbin(i) shows a normalized pixel number of the pixel value i in thehistogram of the G pixel values of the first divisional area ARAk.ARBk_gbin(i) shows a normalized pixel number of the pixel value i in thehistogram of the G pixel values of the second divisional area ARBk.ARAk_bbin(i) shows a normalized pixel number of the pixel value i in thehistogram of the B pixel values of the first divisional area ARAk.ARBk_bbin(i) shows a normalized pixel number of the pixel value i in thehistogram of the B pixel values of the second divisional area ARBk.

The comparison section CP compares the difference SADk to a thresholdand, when the difference SADk is larger than the threshold, determinesthat a distortion correction error occurs in the second divisional areaARB. SADk in the above expression (1) is a real number from 0 to 6 and,when the histograms completely coincide, SADk=0, and the degree ofcoincidence of the histograms is higher as SADk is closer to 0. Thethreshold is set according to the required degree of coincidence of thehistograms. For example, the processing device 200 writes the thresholdin a register (not shown) provided in the circuit device 100 and thecomparison section CP compares the threshold to the difference SADk.

In the above described embodiment, the error detection circuit 320performs detection of the distortion correction error by comparing thehistograms of the pixel values of the input image data IMA in therespective first divisional areas ARA to the histograms of the pixelvalues of the output image data IMB in the respective second divisionalareas ARB.

When the distortion correction error occurs in the second divisionalarea ARB, the histogram of the second divisional area ARB and thehistogram of the first divisional area ARA corresponding thereto do notcoincide. According to the embodiment, the histograms of the respectivefirst divisional areas ARA are compared to the histograms of therespective second divisional areas ARB, and thereby, the area where thehistograms do not coincide may be judged as having the distortioncorrection error. Note that, as described above, the coincidence here isnot limited to a complete coincidence.

Further, in the embodiment, the error detection circuit 320 performsdetection of the distortion correction error by comparing the histogramsof the R pixel values, the histograms of the G pixel values, and thehistograms of the B pixel values of the input image data IMA in therespective first divisional areas ARA to the histograms of the R pixelvalues, the histograms of the G pixel values, and the histograms of theB pixel values of the output image data IMB in the respective seconddivisional areas ARB.

According to the embodiment, the input image data IMA is compared to theoutput image data IMB using the respective RGB histograms, and thereby,accurate error detection can be performed. For example, compared to acase where histograms of luminance values are used, the respective RGBhistograms are used and the histograms are compared includinginformation not only of luminance but also colors.

Furthermore, in the embodiment, the error detection circuit 320normalizes the histograms of the pixel values of the input image dataIMA in the respective first divisional areas ARA by the pixel numbers ofthe respective first divisional areas ARA and normalizes the histogramsof the pixel values of the output image data IMB in the respectivesecond divisional areas ARB by the pixel numbers of the respectivesecond divisional areas ARB. The error detection circuit 320 performsthe detection of the distortion correction error by comparing thenormalized histogram of the pixel values of the input image data IMA tothe normalized histogram of the pixel values of the output image dataIMB.

The output image data IMB is image data after the distortion correction,and the shape of the second divisional area ARB in the output image isdifferent from the shape of the first divisional area ARA set for theinput image. Accordingly, the pixel number of the first divisional areaARA and the pixel number of the second divisional area ARB aredifferent. According to the embodiment, the histograms are normalized bythe pixel numbers of the divisional areas, and thereby, the histogramscan be compared before and after the distortion correction.

3. First to Third Detailed Configuration Examples of Circuit Device

FIG. 6 shows a first detailed configuration example of the circuitdevice 100. In FIG. 6 , the distortion correction circuit 110 includes acoordinate counter 112, a coordinate transformation circuit 113, aninterpolation circuit 114, and a memory circuit 115. Here, an example inwhich the distortion correction circuit 110 is a reverse warp engine isexplained.

The coordinate counter 112 outputs the pixel coordinates GZB=(x,y) onthe output image data IMB. The coordinate transformation circuit 113transforms the pixel coordinates (x,y) into reference coordinatesGZA=(u,v) on the input image data IMA. The memory circuit 115temporarily stores the input image data IMA and outputs pixel data PXDof the reference coordinates (u,v). Specifically, the coordinatetransformation circuit 113 transforms the reference coordinates (u,v)into a read address and the memory circuit 115 reads out the pixel dataPXD of the reference coordinates (u,v) from the read address. Morespecifically, the coordinate transformation circuit 113 outputs the readaddresses of the plurality of pixels around the reference coordinates(u,v) and the memory circuit 115 reads out the pixel data of theplurality of pixels. The interpolation circuit 114 performsinterpolation processing on the plurality of pixel data read out incorrelations with the reference coordinates (u,v) and obtains the pixeldata of the pixel coordinates (x,y) in the output image data IMB.

The area determination unit 321 of the error detection circuit 320determines the first divisional area ARA to which the referencecoordinates GZA=(u,v) on the input image data IMA belong and determinesthe second divisional area ARB to which the pixel coordinates (x,y) onthe output image data IMB belong.

The error determination unit 322 determines whether or not distortioncorrection errors occur in the respective second divisional areas ARB bycalculating histograms from the input image data IMA of the respectivefirst divisional areas ARA and calculating histograms from the outputimage data IMB of the respective second divisional areas ARB based on anarea determination result, and comparing the histograms.

FIG. 7 shows a second detailed configuration example of the circuitdevice 100. In FIG. 7 , the error detection circuit 320 includes thearea determination unit 321, the error determination unit 322, and anerror detection coordinate transformation unit 323.

The error detection coordinate transformation unit 323 transforms thecoordinates GZB (x,y) on the output image data IMB into coordinatesGZA=(u,v) on the input image data IMA. The area determination unit 321determines the first divisional area ARA to which the coordinates GZA onthe input image data IMA belong based on the coordinates GZA, GZB fromthe error detection coordinate transformation unit 323 and determinesthe second divisional area ARB to which the coordinates GZB on theoutput image data IMB belong. The error determination unit 322determines whether or not distortion correction errors occur in therespective second divisional areas ARB by calculating histograms fromthe input image data IMA of the respective first divisional areas ARAand calculating histograms from the output image data IMB of therespective second divisional areas ARB based on an area determinationresult, and comparing the histograms.

FIG. 8 shows a third detailed configuration example of the circuitdevice 100. In FIG. 8 , the error detection circuit 320 includes thearea determination unit 321, the error determination unit 322, and areverse distortion correction unit 324.

The reverse distortion correction unit 324 generates second input imagedata IMA2 by performing a reverse distortion correction as a reversecorrection to the distortion correction performed by the distortioncorrection circuit 110 on the output image data IMB. When the reversedistortion correction is a complete reverse correction, the second inputimage data IMA2 coincide with the input image data IMA. Note that thereverse distortion correction may not be a complete reverse correctiondue to interpolation processing or the like, and the second input imagedata IMA2 may be substantially the same as the input image data IMA. Thearea determination unit 321 determines the first divisional area ARA towhich coordinates GZA2 on the second input image data IMA2 belong. Theerror determination unit 322 calculates histograms from the input imagedata IMA of the respective first divisional areas ARA and calculateshistograms from the second input image data IMA2 of the respective firstdivisional areas ARA based on an area determination result, and comparesthe histograms. The error determination unit 322 determines whether ornot distortion correction errors occur in the respective firstdivisional areas ARA, and thereby, determines whether or not distortioncorrection errors occur in the respective second divisional areas ARBcorresponding thereto.

In the above described embodiment, the circuit device 100 includes aninterrupt signal generation circuit 170 generating an interrupt signalIRQ when the error detection circuit 320 detects the distortioncorrection error.

According to the embodiment, when the error detection circuit 320detects the distortion correction error, the external processing device200 may be informed of the occurrence of the distortion correction errorby the interrupt signal generation circuit 170 generating the interruptsignal IRQ.

Further, in the embodiment, the circuit device 100 includes a statusregister 160 storing the information representing the second divisionalarea ARB where the distortion correction error is detected of the seconddivisional area group.

According to the embodiment, when the detection circuit 320 detects thedistortion correction error, the status register 160 may store theinformation representing the second divisional area ARB where thedistortion correction error is detected of the second divisional areagroup. For example, the external processing device 200 accesses thestatus register 160, and thereby, may grasp the second divisional areaARB where the distortion correction error occurs, i.e., the firstdivisional area ARA where the distortion correction error occurs.

4. Fourth Detailed Configuration Example of Circuit Device

FIG. 9 shows a fourth detailed configuration example of the circuitdevice 100 and a detailed configuration example of the display device 30when the circuit device 100 of the fourth detailed configuration exampleis used. The circuit device 100 of the fourth detailed configurationexample can be combined with any one of the above described first tothird detailed configuration examples.

The display device 30 includes a display panel 20 and a backlight device10. The display panel 20 is a liquid crystal display panel. Thebacklight device 10 is a device radiating backlight to the liquidcrystal display panel. The processing device 200 controls turning on andoff of the backlight device 10 and controls dimming of the backlightdevice 10.

The circuit device 100 includes the input circuit 105, the distortioncorrection circuit 110, the error detection circuit 320, the outputcircuit 130, an interface circuit 140, the status register 160, and theinterrupt signal generation circuit 170.

The interface circuit 140 is a communication interface for theprocessing device 200 to communicate with the circuit device 100. Theinterface circuit 140 is a serial interface of e.g. an SPI standard oran I2C standard. SPI is an abbreviation for Serial Peripheral Interface,and I2C is an abbreviation for Inter-Integrated Circuit.

The error detection circuit 320 writes the information representing thesecond divisional area ARB where the distortion correction error isdetected of the second divisional area group in the status register 160.The information representing the second divisional area ARB where thedistortion correction error is detected may be information representingthe first divisional area ARA corresponding to the second divisionalarea ARB where the distortion correction error is detected.

The interrupt signal generation circuit 170 outputs the interrupt signalIRQ to the processing device 200 when the error detection circuit 320detects the distortion correction error. Specifically, when thedistortion correction errors are detected from one or more seconddivisional areas of the second divisional area group, the interruptsignal generation circuit 170 outputs the interrupt signal IRQ to theprocessing device 200.

When receiving the interrupt signal IRQ, the processing device 200performs processing of dealing with the distortion correction error. Forexample, the processing device 200 may turn off the backlight device ofthe display device 30 or stop transmission of the input image data IMAwhen receiving the interrupt signal IRQ. Alternatively, when receivingthe interrupt signal IRQ, the processing device 200 acquires theinformation representing the second divisional area ARB where thedistortion correction error is detected from the status register 160 viathe interface circuit 140. The processing device 200 performs processingof dealing with the distortion correction error based on the acquiredinformation with respect to each area. As below, examples of theprocessing will be explained.

FIG. 10 shows a first example of processing of dealing with thedistortion correction error with respect to each area. The processingdevice 200 transmits input image data IMA in which the first divisionalarea ARA corresponding to the second divisional area ARB where thedistortion correction error is detected is set to black data to thecircuit device 100. In the HUD display based on the input image dataIMA, the third divisional area ARH corresponding to the first divisionalarea ARA of the black data is transparently displayed.

FIG. 11 shows a second example of the processing of dealing with thedistortion correction error with respect to each area. As shown in theright part of FIG. 11 , the backlight device includes a light emittingelement array and the light emitting element array includes a pluralityof light emitting elements arranged in an array form. Each lightemitting element is a light emitting element that can be controlled tobe independently turned on or off such as an LED. LED is an abbreviationfor Light Emitting Diode. The plurality of light emitting elements arearranged so that, when all of the elements are turned on, the displayarea of the display panel 20 may be illuminated substantially uniformly.The processing device 200 turns off the light emitting elementsilluminating the second divisional area ARB where the distortioncorrection error is detected and turns on the other light emittingelements of the light emitting element array. In the right part of FIG.11 , the turned-off light emitting elements are shown by black circlesand the turned-on light emitting elements are shown by white circles.Thereby, the third divisional area ARH on the HUD display correspondingto the second divisional area ARB where the distortion correction erroris detected is transparent.

In the above described embodiment, the display device 30 includes thedisplay panel 20 and the backlight device 10 for the display panel 20.The processing device 200 controls the backlight device 10 based on thedetection result of the distortion correction error.

According to the embodiment, the processing device 200 may execute theprocessing of dealing with an error based on the detection result of thedistortion correction error output by the circuit device 100. Forexample, the processing device 200 may turn off the backlight device 10when the distortion correction error occurs in one or more seconddivisional areas of the second divisional area group. Alternatively,when the backlight device has the light emitting element array, theprocessing device 200 may turn off the light emitting elementscorresponding to the second divisional area where the distortioncorrection error occurs.

The circuit device of the above described embodiment is used for thehead-up display apparatus. The circuit device includes the distortioncorrection circuit and the error detection circuit. The distortioncorrection circuit performs the distortion correction on the input imagedata as the image data of the input image and outputs the output imagedata as the image data of the output image after the distortioncorrection. When the respective first divisional areas of the firstdivisional area group formed by division of the input image correspondto the respective second divisional areas of the second divisional areagroup in the output image in the distortion correction, the errordetection circuit performs detection of the distortion correction errorof the respective second divisional areas by comparing the input imagedata of the respective first divisional areas to the output image dataof the respective second divisional areas.

According to the embodiment, when the distortion correction error occursin a part of an image, the area where the error occurs may be detected.Specifically, by comparison between the input image data of therespective first divisional areas and the output image data of therespective second divisional areas, the first divisional area and thesecond divisional area at a lower degree of coincidence is detected asthe area where the distortion correction error occurs. Further,according to the embodiment, the output image is a distorted image dueto the distortion correction, and the first divisional area group is setin the undistorted input image. Here, the respective first divisionalareas of the first divisional area group formed by division of the inputimage correspond to the respective second divisional areas of the seconddivisional area group in the output image in the distortion correction,and the error detection circuit may compare the input image data of therespective first divisional areas to the output image data of therespective second divisional areas using the correlations.

Further, in the embodiment, the error detection circuit may determinecorrelations between the respective first divisional areas and therespective second divisional areas based on the correlation informationbetween the coordinates on the input image and the coordinates on theoutput image correlated by the distortion correction.

According to the embodiment, the coordinate transformation between thecoordinates on the input image and the coordinates on the output imageis performed in the coordinate transformation of the distortioncorrection. The error detection circuit may determine the firstdivisional area to which the coordinates on the input imagecorresponding to the coordinates on the output image belong using thecorrelations. Thereby, the first divisional areas on the input image andthe second divisional areas on the output image are correlated.

Furthermore, in the embodiment, the error detection circuit may performdetection of the distortion correction error by comparing the histogramsof the pixel values of the input image data in the respective firstdivisional areas to the histograms of the pixel values of the outputimage data in the respective second divisional areas.

When the distortion correction error occurs in the second divisionalarea, the histogram of the second divisional area and the histogram ofthe first divisional area corresponding thereto do not coincide.According to the embodiment, the histograms of the respective firstdivisional areas are compared to the histograms of the respective seconddivisional areas, and thereby, the area where the histograms do notcoincide may be judged as having the distortion correction error.

In the embodiment, the error detection circuit may perform detection ofthe distortion correction error by comparing the histograms of the Rpixel values, the histograms of the G pixel values, and the histogramsof the B pixel values of the input image data in the respective firstdivisional areas to the histograms of the R pixel values, the histogramsof the G pixel values, and the histograms of the B pixel values of theoutput image data in the respective second divisional areas.

According to the embodiment, the input image data is compared to theoutput image data using the respective RGB histograms, and thereby,accurate error detection can be performed. For example, compared to acase where histograms of luminance values are used, the respective RGBhistograms are used and the histograms are compared includinginformation not only of luminance but also colors.

Furthermore, in the embodiment, the error detection circuit maynormalize the histograms of the pixel values of the input image data inthe respective first divisional areas by the pixel numbers of therespective first divisional areas and normalize the histograms of thepixel values of the output image data in the respective seconddivisional areas by the pixel numbers of the respective seconddivisional areas. The error detection circuit may perform the detectionof the distortion correction error by comparing the normalized histogramof the pixel values of the input image data to the normalized histogramof the pixel values of the output image data.

The output image data is image data after the distortion correction, andthe shape of the second divisional area in the output image is differentfrom the shape of the first divisional area set for the input image.Accordingly, the pixel number of the first divisional area ARA and thepixel number of the second divisional area are different. According tothe embodiment, the histograms are normalized by the pixel numbers ofthe divisional areas, and thereby, the histograms can be compared beforeand after the distortion correction.

In the embodiment, the circuit device may include the interrupt signalgeneration circuit generating the interrupt signal when the distortioncorrection error is detected by the error detection circuit.

According to the embodiment, when the distortion correction error isdetected by the error detection circuit, the interrupt signal generationcircuit generates the interrupt signal, and thereby, the externalprocessing device may be informed of the occurrence of the distortioncorrection error.

Further, in the embodiment, the circuit device may include the statusregister storing the information representing the second divisional areawhere the distortion correction error is detected of the seconddivisional area group.

According to the embodiment, when the distortion correction error isdetected by the error detection circuit, the status register may storethe information representing the second divisional area where thedistortion correction error is detected of the second divisional areagroup. For example, the external processing device accesses the statusregister, and thereby, may grasp the second divisional area where thedistortion correction error occurs, i.e., the first divisional areawhere the distortion correction error occurs.

The head-up display apparatus of the embodiment includes the circuitdevice according to one of the above described circuit devices, theprocessing device controlling the circuit device, and the display deviceprojecting the display image based on the output image data from thecircuit device.

In the embodiment, the display device may include the display panel andthe backlight device for the display panel. The processing device maycontrol the backlight device based on the detection result of thedistortion correction error.

According to the embodiment, the processing device may execute theprocessing of dealing with an error based on the detection result of thedistortion correction error output by the circuit device. For example,the processing device may turn off the backlight device when thedistortion correction error occurs in one or more second divisionalareas of the second divisional area group. Alternatively, when thebacklight device has the light emitting element array, the processingdevice may turn off the light emitting elements corresponding to thesecond divisional area where the distortion correction error occurs.

Note that the embodiments are explained in detail as described above,however, a person skilled in the art could easily understand that manymodifications without substantively departing from the new matter andthe effects of the present disclosure can be made. Therefore, the scopeof the present disclosure includes all of these modified examples. Forexample, in the specification or the drawings, terms described withdifferent terms in a broader sense or synonymous at least once may bereplaced by the different terms in any part of the specification or thedrawings. Further, the scope of the present disclosure includes allcombinations of the embodiments and modified examples. Furthermore, theconfigurations, the operations, etc. of the circuit device, the head-updisplay apparatus, the processing device, the display system, etc. arenot limited to those explained in the embodiments, but variousmodifications can be made.

What is claimed is:
 1. A circuit device used for a head-up displayapparatus, comprising: a distortion correction circuit performing adistortion correction on input image data as image data of an inputimage and outputting output image data as image data of an output imageafter the distortion correction; and an error detection circuit, whenrespective first divisional areas of a first divisional area groupformed by division of the input image correspond to respective seconddivisional areas of a second divisional area group in the output imagein the distortion correction, performing detection of a distortioncorrection error of the respective second divisional areas by comparingthe input image data of the respective first divisional areas to theoutput image data of the respective second divisional areas.
 2. Thecircuit device according to claim 1, wherein the error detection circuitdetermines correlations between the respective first divisional areasand the respective second divisional areas based on correlationinformation of coordinates on the input image and coordinates on theoutput image correlated by the distortion correction.
 3. The circuitdevice according to claim 1, wherein the error detection circuitperforms detection of the distortion correction error by comparinghistograms of pixel values of the input image data in the respectivefirst divisional areas to histograms of pixel values of the output imagedata in the respective second divisional areas.
 4. The circuit deviceaccording to claim 3, wherein the error detection circuit performsdetection of the distortion correction error by comparing histograms ofR pixel values, histograms of G pixel values, and histograms of B pixelvalues of the input image data in the respective first divisional areasto histograms of R pixel values, histograms of G pixel values, andhistograms of B pixel values of the output image data in the respectivesecond divisional areas.
 5. The circuit device according to claim 3,wherein the error detection circuit normalizes the histograms of thepixel values of the input image data in the respective first divisionalareas by pixel numbers of the respective first divisional areas andnormalizes the histograms of the pixel values of the output image datain the respective second divisional areas by pixel numbers of therespective second divisional areas, and performs detection of thedistortion correction error by comparing the normalized histogram of thepixel values of the input image data to the normalized histogram of thepixel values of the output image data.
 6. The circuit device accordingto claim 1, further comprising an interrupt signal generation circuitgenerating an interrupt signal when the distortion correction error isdetected by the error detection circuit.
 7. The circuit device accordingto claim 6, further comprising a status register storing informationrepresenting the second divisional area where the distortion correctionerror is detected of the second divisional area group.
 8. A head-updisplay apparatus comprising: the circuit device according to claim 1; aprocessing device controlling the circuit device; and a display deviceprojecting a display image based on the output image data from thecircuit device.
 9. The head-up display apparatus according to claim 8,wherein the display device includes a display panel and a backlightdevice for the display panel, and the processing device controls thebacklight device based on a detection result of the distortioncorrection error.